This invention relates to a glass-ceramic composite material for use in a flat packaged piezoelectric device. This invention relates also to the flat packaged piezoelectric device.
A flat packaged piezoelectric device of the type described is, for example, a crystal oscillator unit or an SAW (surface acoustic wave) resonator unit and is for use in surface mounting.
A conventional flat packaged piezoelectric device comprises a base member, a pair of electrode pad parts formed on the base member, and a piezoelectric oscillator piece of, for example, a quartz piece. A pair of electrodes are formed on both surfaces of the piezoelectric oscillator piece and have parts fixed to the electrode pad parts. A cap member is sealed air-tight to the base member to enclose the piezoelectric oscillator piece in cooperation with the base member.
As will later be described, the piezoelectric oscillator piece and the base and the cap members have a difference in thermal expansion coefficients. This gives rise to a strain after cooling down from a raised temperature to result in a variation in the resonance frequency of the crystal oscillator unit and to make it impossible to attain a desired frequency characteristic.
Moreover, use of a resilient supporter as intermediary for connection of the piezoelectric oscillator piece to the base and the cap members in solving the above-described problem, results in other problems, such as an increased manufacturing cost and a thicker thickness of the flat packaged piezoelectric device as will also later be described.
Still further, alumina (Al.sub.2 O.sub.3) for use as a principal material of each of the base and the cap members must be sintered at a temperature of 1500.degree. to 1600.degree. C. As a consequence, internal conductors for wiring in the flat packaged piezoelectric device must be made of tungsten (W), molybdenum (Mo), and a like metal having a high melting point if the conductors should concurrently be sintered. Such a metal of the high melting point has a low electric conductivity and is not adapted to soldering. Nickel (Ni) plating and/or gold (Au) plating are therefore indispensable. As a result, great amounts of process and cost are necessary on manufacture.